The Confederate States in 1862 in dark green. Light green denotes claims made by the Confederacy. Medium green denotes western counties of Virginia that separated from that State and were admitted to the Union as West Virginia. Teal denotes the still contested Indian Territory.

Each state declared its secession from the United States, which became known as the Union during the ensuing civil war, following the November 1860 election of Republican candidate Abraham Lincoln to the U.S. presidency on a platform which opposed the expansion of slavery into the western territories. Before Lincoln took office in March, a new Confederate government was established in February 1861, which was considered illegal by the government of the United States. States volunteered militia units and the new government hastened to form its own Confederate States Army from scratch practically overnight. After the American Civil War began in April, four slave states of the Upper South—Virginia, Arkansas, Tennessee, and North Carolina—also declared their secession and joined the Confederacy. The Confederacy later accepted Missouri and Kentucky as members, although neither officially declared secession nor were they ever largely controlled by Confederate forces; Confederate shadow governments attempted to control the two states but were later exiled from them.

The government of the United States (the Union) rejected the claims of secession and considered the Confederacy illegally founded. The War began with the Confederate attack upon Fort Sumter on April 12, 1861, a Union fort in the harbor of Charleston, South Carolina. No foreign government officially recognized the Confederacy as an independent country,[1][3][4] although Great Britain and France granted it belligerent status, which allowed Confederate agents to contract with private concerns for arms and other supplies. In early 1865, after four years of heavy fighting which led to 620,000-850,000 military deaths,[5][6] all the Confederate forces surrendered and the Confederacy vanished. The war lacked a formal end; nearly all Confederate forces had been forced into surrender or deliberately disbanded by the end of 1865, by which point the dwindling manpower and resources of the Confederacy were facing overwhelming odds.[2] By 1865, Jefferson Davis lamented that the Confederacy had "disappeared".[7]

Missouri and Kentucky were represented by partisan factions adopting the forms of state governments without control of substantial territory or population in either case. The antebellum state governments in both maintained their representation in the Union. Also fighting for the Confederacy were two of the "Five Civilized Tribes" – the Choctaw and the Chickasaw – in Indian Territory and a new, but uncontrolled, Confederate Territory of Arizona. Efforts by certain factions in Maryland to secede were halted by federal imposition of martial law; Delaware, though of divided loyalty, did not attempt it. A Unionist government was formed in opposition to the secessionist state government in Richmond and administered the western parts of Virginia that had been occupied by Federal troops. The Restored Government later recognized the new state of West Virginia, which was admitted to the Union during the war on June 20, 1863, and re-located to Alexandria for the rest of the war.[9]

Confederate control over its claimed territory and population in congressional districts steadily shrank from 73% to 34% during the course of the American Civil War due to the Union's successful overland campaigns, its control of the inland waterways into the South, and its blockade of the southern coast.[10] With the Emancipation Proclamation on January 1, 1863, the Union made abolition of slavery a war goal (in addition to reunion). As Union forces moved southward, large numbers of plantation slaves were freed. Many joined the Union lines, enrolling in service as soldiers, teamsters and laborers. The most notable advance was Sherman's "March to the Sea" in late 1864. Much of the Confederacy's infrastructure was destroyed, including telegraphs, railroads and bridges. Plantations in the path of Sherman's forces were severely damaged. Internal movement became increasingly difficult for Southerners, weakening the economy and limiting army mobility.[11]

These losses created an insurmountable disadvantage in men, materiel, and finance. Public support for Confederate President Jefferson Davis's administration eroded over time due to repeated military reverses, economic hardships, and allegations of autocratic government. After four years of campaigning, Richmond was captured by Union forces in April 1865. A few days later General Lee surrendered to Union General Ulysses S. Grant, effectively signalling the collapse of the Confederacy. President Davis was captured on May 10, 1865, and jailed in preparation for a treason trial that was ultimately never held.[12]